It counts down your lifespan, to the last second, so you know how long you have left.
The intent behind Tikker is to remind you that time is precious, and thus not to be wasted on negativity.
Tikker
Here's how it "knows" how long you have left:
The wearer simply fills out a questionnaire, deducts his/her current age from the results, and TIKKER is ready to start the countdown.
The company founder, Fredrik Colting, is trying to raise $25,000 on Kickstarter to fund full-scale production.
It's certainly cool-looking: